1. Field of the Invention
The present invention relates to a tire condition monitoring system for use in an automotive vehicle, the system wirelessly detecting tire conditions including pressure and temperature in a tire.
2. Description of Related Art
A tire condition monitoring system, in which tire conditions such as pressure and temperature in each tire are detected and the data are wirelessly transmitted to an on-board monitor, has been known hitherto. The detected data transmitted to the monitor are informed to a driver of the vehicle to enhance driving safety. Generally, in this kind of monitoring system, a detector installed in each tire is automatically and periodically activated even when detected data are not required. Therefore, energy consumption in the detectors become high, and a battery having a high capacity has to be installed to each detector. In addition, the detected data may be simultaneously transmitted from plural detectors to the monitor, causing confusion among the data.
To cope with those problems, an improved system is proposed by JP-A-8-244423. In this system, an identification code is assigned to a detector installed in each tire, and a particular detector selectively activated. In this manner, power consumption in the detector can be lowered, and simultaneous data transmission from plural detectors is avoided. Another proposal has been made in JP-A-2001-250186. In this proposed system, a signal for initiating operation of the detectors is sent when an engine is started, and the operation of the detector is terminated when the engine is stopped.
In those proposed systems, however, the following problems are involved. When other vehicles having a monitoring system similar to his own system come close to his own vehicle, detectors of other vehicles may be actuated simultaneously with his own detectors based on the initiation signal wirelessly transmitted from a transmitter of his own vehicle or other vehicles. If this happens, data detected by detectors of other vehicles, which are wirelessly transmitted, may be received by the monitor of his own vehicle, causing confusion with the data detected by the detector of his own vehicle. This trouble may be caused by the detector signals from other vehicles when his monitor does not send the initiation signal to his detector. Further, though it is conventionally proposed to decrease the power consumption in the detectors by operating the detectors for a limited time period, the amount of power saved in that method is not sufficiently large.